1. Field of the Invention
The present invention relates to a printing tape through which images such as characters are printed thereon by being heated through a thermal head, and in particular, relates to a printing tape, on a top surface of which a colored transparent layer defining background color of the printing tape is formed so that images such as characters can be clearly recognized in the background color and which can be adhered onto an object after printing of images is conducted. And the present invention relates to a printing-tape cassette or cartridge accommodating the above printing tape, which is utilized in a tape printer.
2. Description of Related Art
Conventionally, there have been proposed various printing tapes. These kinds of printing tapes are generally produced by forming a heat-sensitive or thermal chromogenic layer on a film-like support sheet. Here, for instance, in order to form the heat-sensitive or thermal chromogenic layer, a mixture of leuco-dye such as crystal violet lactone (CVL), which is disclosed in the specifications of U.S. Pat. Nos. 2,712,507 and 2,730,457, and organic acid such as phenol compound, is used.
On the surface of the heat-sensitive or thermal chromogenic layer, a protection layer for protecting the heat-sensitive or thermal chromogenic layer is formed and the protection layer is made transparent so that colored portions (i.e. images such as characters) can be visually recognized through the protection layer.
Further, on the surface of the support sheet opposite to the surface where the heat-sensitive or thermal chromogenic layer is formed, a colored layer is formed by coating print ink, which includes pigments or dyes, so that the images formed in the heat-sensitive or thermal chromogenic layer can be recognized in the background color defined by the colored layer. At that time, the background color of the colored layer is visually recognized through the support sheet, the heat-sensitive or thermal chromogenic layer and the protection layer.
In the thus produced printing tape, the heat-sensitive or thermal chromogenic layer is colored by being heated through a thermal head, thereby the image such as characters are formed in the background color defined by the colored layer, on the printing tape. And, in general, the printing tape is utilized in a tape printer in a state that the printing tape is accommodated in a printing-tape cartridge. In the case that printing of the images is conducted on the printing tape through the thermal head arranged in the tape printer, the heat-sensitive or thermal chromogenic layer is heated by the thermal head while both the thermal head and the printing tape are relatively moved. Thereby, the images such as characters are printed on the printing tape.
However, the heat-sensitive or thermal chromogenic layer formed from the mixture mentioned above is generally translucent and it is very difficult to make the heat-sensitive or thermal chromogenic layer transparent. Therefore, the background color of the colored layer recognized through the translucent chromogenic layer becomes blurred and whitened color, due to translucency of the heat-sensitive or thermal chromogenic layer such as frosted glass. As a result, inherent color of pigments or dyes in the colored layer cannot be seen. Clearly from the above, unless the support sheet, the heat-sensitive or thermal chromogenic layer and the protection layer are transparent, the background color of the colored layer formed cannot be recognized therethrough, so long as the colored layer is formed on the surface of the support sheet opposite to the surface where the heat-sensitive or thermal chromogenic layer is formed.